Haploid cells are cells that contain only one set of chromosomes. In humans, these would be sperm or egg cells.
Diploid Cells: Cells containing two sets of chromosomes; one from each parent.
Gametes: Sex cells (sperm or eggs) which are haploid and combine during fertilization to create a new organism with a full set of genes.
Zygote: A diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum.